Method and system for engine cooling system control

ABSTRACT

Methods and systems are providing for improving engine coolant level estimation to reduce engine overheating. The level of fluid in a coolant overflow reservoir is inferred based on the fluid level in a hollow vertical standpipe fluidically coupled to the reservoir at top and bottom locations, while the fluid level in the standpipe is estimated based on echo times of an ultrasonic signal transmitted by a sensor positioned in a recess at the bottom of the vertical standpipe. Engine power is limited differently based on distinct coolant level states determined based on a change in level of coolant in the reservoir over a duration.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 14/583,393 entitled “METHOD AND SYSTEM FOR ENGINE COOLING SYSTEMCONTROL,” filed on Dec. 26, 2014. The entire contents of theabove-referenced application are hereby incorporated by reference intheir entirety for all purposes.

FIELD

The present application relates to methods and systems for inferring afluid level in a coolant overflow container (or degas bottle), andadjusting engine operation, based on a fluid level estimated in avertical hollow standpipe fluidically coupled to the overflow container.

BACKGROUND AND SUMMARY

Vehicles may include cooling systems configured to reduce overheating ofan engine by transferring the heat to ambient air. Therein, coolant iscirculated through the engine block to remove heat from the engine, theheated coolant then circulated through a radiator to dissipate the heat.The cooling system may include various components such as a coolantreservoir coupled to the system for degassing and storing coolant. Apressurized reservoir that also serves to separate entrained air fromthe coolant is typically called a degas bottle. When the temperature ofcoolant anywhere in the system rises, thermal expansion of the coolantcauses pressure to rise in the degas bottle as the trapped air volumereduces. Pressure relief can be achieved by releasing air from the degasbottle through a valve that is typically mounted in the fill cap. Then,when the temperature and pressure of coolant drops below atmosphericpressure in the degas bottle, air may be drawn back into the bottlethrough another valve that is often mounted in the fill cap.

If the coolant level in bottle is too low, the air volume will be toolarge to build sufficient pressure to prevent boiling and cavitation atthe water pump inlet. At low fluid levels, the degas bottle will also nolonger be able to separate air from the coolant and air can be drawninto the cooling system, again leading to poor cooling performance. Ifan overflow system is employed instead of an active degas system, asimilar loss in cooling system performance can be realized when fluidlevels are low.

Various approaches may be used to estimate fluid level in a reservoir.One example approach described by Murphy in U.S. Pat. No. 8,583,387 usesan ultrasonic fluid level sensor installed at the bottom of a reservoirto estimate a fluid level of the reservoir. However, the inventorsherein have recognized that in such a cooling system, the dimensions ofthe coolant reservoir may vary based on the temperature of coolantcontained in the reservoir. As a result, there may be inconsistencies inthe estimated coolant level. Additionally, due to the location of thesensor at the bottom of the container, at low coolant levels, it may beunclear whether the fluid level in the reservoir is low or empty.Further still, it may be difficult to differentiate actual low coolantlevels from incorrect coolant level estimation due to sensordegradation. In another example approach, described by Gordon et al inUS 20130103284, the sensor is coupled to a coolant reservoir hose. Oneissue with such an approach is that the sensor can only detect thepresence of coolant at that location in the circuit. Critical componentsof the power train may not be receiving coolant despite the presence ofcoolant in one of the coolant reservoir hoses, particularly if that hoseis isolated from the cooling system by a valve (e.g., the enginethermostat hose). Further, while an indication of low coolant fluidlevel is received, engine temperature control may already be degradeddue to substantial emptying of the coolant reservoir.

In one example, the above issues may be at least partly addressed by amethod for a coolant system, comprising: estimating fluid level in acoolant reservoir based on a sensor coupled in a vertical standpipealigned parallel to the reservoir, the standpipe fluidically coupled tothe reservoir at each of a top and bottom location; and limiting enginepower based on the estimated fluid level. In this way, changes incoolant level state based on transient changes in estimated coolantlevel may be reduced, and appropriate measures may be taken to avoidengine overheating when the coolant level state is empty versus low, orif the sensor has been faulted or degraded for longer than a thresholdduration.

As one example, an engine coolant system may include a vertical tubealigned with a coolant overflow reservoir, the tube housing anultrasonic sensor. The vertical tube may be coupled to the coolantreservoir at each of a top and bottom location via hoses, coolantflowing between the tube and the reservoir via the hoses. The hoses maybe connected such that a headspace is generated between the top of thefluid level in the vertical tube and the top of the tube. In addition,the hoses may be connected such that the top of the vertical tube isarranged at a lower height than the top of the coolant reservoir,thereby allowing the sensor to more reliably estimate the fluid level inthe reservoir and distinguish between low and empty coolant levelstates. The sensor, positioned inside a recess at the bottom of thevertical tube, may transmit a signal to the top of the vertical tube, anecho of the signal being received at the sensor after being reflectedoff the top of the tube. The signal may be transmitted periodically andbased on an average echo time (which is the time elapsed between thesignal being transmitted and an echo of the signal being received), thecoolant level in the vertical tube may be estimated. This estimate maythen be used to infer the coolant level in the reservoir. Changes incoolant level state may then be performed based on a change in coolantreservoir fluid level over a threshold duration. This allows the coolantlevel state to be updated only after the fluid level estimate hasstabilized. Diagnostic codes may then be set based on the coolant levelstate. Further, engine power may be limited to different degrees basedon the coolant level state. As an example, in response to an indicationof low coolant level, a first diagnostic code may be set and engine loadmay be limited by a first amount to reduce engine overheating. Inaddition, fuel injection may be disabled for a duration to reduce theamount of heat transferred to the engine coolant. The first diagnosticcode may be cleared upon completion of the key cycle. If a time elapsedsince entering the first diagnostic mode exceeds a threshold duration,and the coolant state is still low, or has changed to EMPTY, a seconddiagnostic code may be set and engine power may be limited by a second,larger amount. For example, in the second diagnostic mode, the enginemay be forced to operate at idle. In addition, the second diagnosticcode may not be cleared until the vehicle is taken to a servicetechnician and a dealer code has been entered.

In this way, an accuracy and reliability of determining a coolant levelof a coolant overflow reservoir can be increased. By inferring thecoolant level of the reservoir based on an estimated coolant level of astandpipe coupled to the reservoir, inaccuracies in coolant levelestimation due to distortion of an in-tank sensor output during thermalfluctuations, or vehicle motion, is reduced. By updating the coolantlevel state of the coolant overflow reservoir selectively based onchanges in coolant level at the standpipe of the over duration, frequentand erratic coolant level estimation can be reduced. In addition,unintentional triggering of an engine failure mode is reduced. As such,this reduces the frequency with which engine output is unnecessarilylimited. By relying on an ultrasonic sensor and the local processor toestimate the coolant level of the standpipe based on an echo time,coolant level estimation can be expedited. Overall, engine overheatingdue to inaccurate coolant level estimation can be reduced.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 shows an engine system including an engine cooling system.

FIG. 2 shows a block diagram of an engine cooling system.

FIG. 3 shows part of an example cooling system, including a coolantreservoir fluidly coupled to a standpipe, the standpipe affixed to thevehicle frame.

FIG. 4 shows an alternate view of the part of the cooling system in FIG.3, highlighting features of the fluid coupling and of the affixing ofthe standpipe.

FIG. 5 shows a second alternate view of the part of the cooling systemin FIG. 3.

FIG. 6 shows a third alternate view of the part of the cooling system inFIG. 3, highlighting the affixing of the standpipe to the vehicle frame.

FIG. 7 shows a fourth alternate view of the part of the cooling systemin FIG. 3, highlighting an ultrasonic level sensor within the standpipeand the affixing of the standpipe to the vehicle frame.

FIG. 8 shows a cap configured to fit on the top of a vertical standpipe.

FIG. 9 shows a high-order flowchart for estimating a level of fluid inthe coolant reservoir.

FIG. 10 depicts an example method for adjusting the amount of powersupplied to an ultrasonic level sensor in a vertical standpipe of acooling system.

FIG. 11 depicts an example method for estimating a fluid level in avertical standpipe based on information from an ultrasonic level sensor.

FIG. 12 depicts an example method for estimating a fluid level in avertical standpipe based on echo times and a fluid composition estimate.

FIGS. 13A-13C show the divergence of the fluid levels in the verticalstandpipe and the coolant reservoir based on vehicle attitude.

FIG. 14 depicts an example method for determining a slosh term andadjusting a standpipe fluid level estimate based on the slosh term.

FIG. 15 depicts an example method for detecting degradation of theultrasonic level sensor based on accumulated slosh terms.

FIG. 16 depicts an example control system for determining a slosh termand adjusting a bulk coolant level estimate based on the slosh term.

FIG. 17 shows four instances of slosh within a standpipe compared topredicted amounts of slosh.

FIG. 18 depicts an example method for determining a coolant level basedon comparing a bulk coolant level estimate to various thresholds.

FIG. 19 depicts determining a coolant state based on a history ofcoolant levels and coolant states.

DETAILED DESCRIPTION

The following description relates to systems and methods for controllingan engine of a vehicle, the engine having a cooling system such as thatof FIGS. 1-2. The cooling system may include a coolant overflowreservoir, herein also referred to as a degas bottle, fluidly connectedto a narrow vertical standpipe, as discussed at FIGS. 3-8. The verticalstandpipe may include a level sensor broadcasting information to anengine controller for determining an amount of coolant within thestandpipe, as elaborated at FIGS. 9-12. The controller may also estimatean amount of coolant within the degas bottle (herein also referred to asa bulk coolant level), based on the amount of coolant within thestandpipe (herein also referred to as a local coolant level) and variousmotion parameters, as described at FIGS. 13-17. Based on the estimate ofcoolant, the controller may indicate a coolant state, and based on thecoolant state, restrictions may be placed on engine operatingparameters, as discussed at FIGS. 18-19. In this way, bulk coolantlevels may be inferred more accurately even during slosh events. Inaddition, low coolant levels may be more reliably detected and engineoperating parameters may be restricted accordingly to preventoverheating of the engine.

FIG. 1 shows an example embodiment of a vehicle system 100 including avehicle cooling system 101 in a motor vehicle 102. Vehicle 102 has drivewheels 106, a passenger compartment 104 (herein also referred to as apassenger cabin), and an under-hood compartment 103. Under-hoodcompartment 103 may house various under-hood components under the hood(not shown) of motor vehicle 102. For example, under-hood compartment103 may house internal combustion engine 10. Internal combustion engine10 has a combustion chamber which may receive intake air via intakepassage 44 and may exhaust combustion gases via exhaust passage 48.Engine 10 as illustrated and described herein may be included in avehicle such as a road automobile, among other types of vehicles. Whilethe example applications of engine 10 will be described with referenceto a vehicle, it should be appreciated that various types of engines andvehicle propulsion systems may be used, including passenger cars,trucks, etc.

Under-hood compartment 103 may further include cooling system 101 thatcirculates coolant through internal combustion engine 10 to absorb wasteheat, and distributes the heated coolant to radiator 80 and/or heatercore 90 via coolant lines (or loops) 82 and 84, respectively. In oneexample, as depicted, cooling system 101 may be coupled to engine 10 andmay circulate engine coolant from engine 10 to radiator 80 viaengine-driven water pump 86, and back to engine 10 via coolant line 82.Engine-driven water pump 86 may be coupled to the engine via front endaccessory drive (FEAD) 36, and rotated proportionally to engine speedvia a belt, chain, etc. Specifically, engine-driven pump 86 maycirculate coolant through passages in the engine block, head, etc., toabsorb engine heat, which is then transferred via the radiator 80 toambient air. In one example, where pump 86 is a centrifugal pump, thepressure (and resulting flow) produced by the pump may be increased withincreasing crankshaft speed, which in the example of FIG. 1, may bedirectly linked to the engine speed. In some examples, engine-drivenpump 86 may operate to circulate the coolant through both coolant lines82 and 84.

The temperature of the coolant may be regulated by a thermostat 38.Thermostat 38 may include a temperature sensing element 238, located atthe junction of cooling lines 82, 85, and 84. Further, thermostat 38 mayinclude a thermostat valve 240 located in cooling line 82. As elaboratedin further detail at FIG. 2, the thermostat valve remain closed untilthe coolant reaches a threshold temperature, thereby limiting coolantflow through the radiator until the threshold temperature is reached.

Coolant may flow through coolant line 84 to heater core 90 where theheat may be transferred to passenger compartment 104. Then, coolantflows back to engine 10 through valve 122. Specifically, heater core 90,which is configured as a water-to-air heat exchanger, may exchange heatwith the circulating coolant and transfer the heat to the vehiclepassenger compartment 104 based on operator heating demands. As such,heater core may also be coupled to a vehicle HVAC system (or heating,ventilation, and air conditioning system) that includes other componentssuch as a heater fan, and an air conditioner (not shown).

Based on a cabin heating/cooling request received from the operator, theHVAC system may warm cabin air using the heated coolant at the heatercore to raise cabin temperatures and provide cabin heating. One or moreblowers (not shown) and cooling fans may be included in cooling system101 to provide airflow assistance and augment a cooling airflow throughthe under-hood components. For example, cooling fan 92, coupled toradiator 80, may be operated to provide cooling airflow assistancethrough radiator 80. Cooling fan 92 may draw a cooling airflow intounder-hood compartment 103 through an opening in the front-end ofvehicle 102, for example, through grill shutter system 112. Such acooling air flow may then be utilized by radiator 80 and otherunder-hood components (e.g., fuel system components, batteries, etc.) tokeep the engine and/or transmission cool. Further, the air flow may beused to reject heat from a vehicle air conditioning system. Furtherstill, the airflow may be used to improve the performance of aturbocharged/supercharged engine that is equipped with intercoolers thatreduce the temperature of the air that goes into the intakemanifold/engine. In one example, grill shutter system 112 may beconfigured with a plurality of louvers (or fins, blades, or shutters)wherein a controller may adjust a position of the louvers to control anairflow through the grill shutter system.

Cooling fan 92 may be coupled to, and driven by, engine 10, viaalternator 72 and system battery 74. Cooling fan 92 may also bemechanically coupled to engine 10 via an optional clutch (not shown).During engine operation, the engine generated torque may be transmittedto alternator 72 along a drive shaft (not shown). The generate torquemay be used by alternator 72 to generate electrical power, which may bestored in an electrical energy storage device, such as system battery74. Battery 74 may then be used to operate an electric cooling fan motor94.

Vehicle system 100 may further include a transmission 40 fortransmitting the power generated at engine 10 to vehicle wheels 106.Transmission 40, including various gears and clutches, may be configuredto reduce the high rotational speed of the engine to a lower rotationalspeed of the wheel, while increasing torque in the process. To enabletemperature regulation of the various transmission components, coolingsystem 101 may also be communicatively coupled to a transmission coolingsystem 45. The transmission cooling system 45 includes a transmissionoil cooler 125 (or oil-to-water transmission heat exchanger) locatedinternal or integral to the transmission 40, for example, in thetransmission sump area at a location below and/or offset from thetransmission rotating elements. Transmission oil cooler 125 may have aplurality of plate or fin members for maximum heat transfer purposes.Coolant from coolant line 84 may communicate with transmission oilcooler 125 via conduit 46. In comparison, coolant from coolant line 82and radiator 80 may communicate with transmission oil cooler 125 viaconduit 48.

FIG. 1 further shows a control system 14. Control system 14 may becommunicatively coupled to various components of engine 10 to carry outthe control routines and actions described herein. For example, as shownin FIG. 1, control system 14 may include an electronic digitalcontroller 12. Controller 12 may be a microcomputer, including amicroprocessor unit, input/output ports, an electronic storage mediumfor executable programs and calibration values, random access memory,keep alive memory, and a data bus. As depicted, controller 12 mayreceive input from a plurality of sensors 16, which may include userinputs and/or sensors (such as transmission gear position, gas pedalinput, brake input, transmission selector position, vehicle speed,vehicle acceleration, vehicle attitude, engine speed, mass airflowthrough the engine, ambient temperature, intake air temperature, etc.),cooling system sensors (such as coolant temperature, coolant level,coolant level sensor circuit board temperature, cylinder heattemperature, fan speed, passenger compartment temperature, ambienthumidity, thermostat output, etc.), and others. Further, controller 12may communicate with various actuators 18, which may include engineactuators (such as fuel injectors, an electronically controlled intakeair throttle plate, spark plugs, etc.), cooling system actuators (suchas the various valves of the cooling system), and others. In someexamples, the storage medium may be programmed with computer readabledata representing instructions executable by the processor forperforming the methods described below as well as other variants thatare anticipated but not specifically listed.

Now turning to FIG. 2, it shows an example embodiment 200 of the coolingsystem of FIG. 1 with the various valves, loops, and heat exchangers.

Coolant may be circulated at thermostat 38 from various loops. As such,thermostat 38 is configured with a temperature sensing element 238 forestimating a temperature of coolant circulating at the thermostat, whilethermostat valve 240, communicatively coupled to the temperature sensingelement, is configured to open only when the temperature is above athreshold. In one example, thermostat valve 240 may be a mechanicallyactuated valve, such as a wax plug for the actuation force/displacement,that opens when coolant sensed at the temperature sensing element (thewax) is above the threshold temperature.

Coolant may circulate along a first bypass loop 220 from engine 10towards thermostat 38. From there, the coolant may be pumped back to theengine by pump 86. Coolant may also circulate along a second heater loop222 from engine 10 via heater core 90 and engine oil cooler 225 towardsthermostat 38. From there, the coolant may be pumped back to the engineby pump 86. Coolant may also circulate from engine 10, through radiator80, via third loop 224, to thermostat 38, based on the state of thethermostat valve 240. Specifically, when thermostat valve 240 is open,coolant may circulate though radiator 80, and then through thermostatvalve 240. The flow of coolant through the radiator may allow heat fromthe circulating hot coolant to be dissipated to the ambient air by theradiator fan. After flowing through the thermostat valve, coolant may bepumped back towards the engine by pump 86. Coolant may circulate along afourth coolant loop 226 from one of radiator 80 and water outlet 204,through transmission oil cooler 125, and then to engine oil cooler 225.

Coolant may flow from water outlet 204 and radiator 80 toward degasbottle 208, which may serve as a coolant reservoir within cooling system200. Degas bottle 208 may be fluidly connected to vertically-orientedstandpipe 210 via upper level sensor hose 214 and lower level sensorhose 216, as further described in reference to FIGS. 3-7. Upper levelsensor hose may connect the top of degas bottle 208 to the top ofvertical standpipe 210, and may be configured to allow air to flowbetween the two. Lower level sensor hose 216 may be connected to degasbottle 208 via degas bottle outlet hose 216, and may be configured toallow coolant to flow between degas bottle 208 and vertical standpipe210. Vertical standpipe 210 may include a piezoelectric coolant levelsensor 212, electronically connected to controller 12.

When the fluid in the cooling system heats up, it expands, causing thepressure to build up. For cooling systems with overflow bottles, theradiator cap may be the only place where this pressure can escape. Assuch, the setting of the spring on the radiator cap determines themaximum pressure in the cooling system. When the pressure reaches 15psi, for example, the pressure pushes a valve of the radiator cap open,allowing pressurized coolant to escape from the cooling system. Thiscoolant flows through the overflow tube of the radiator into theoverflow bottle. Thus, this arrangement keeps air out of the coolantsystem. When the radiator cools back down, a vacuum is created in thecooling system that pulls open a spring loaded valve, sucking coolantback in from the bottom of the overflow bottle into the radiator.

While overflow systems control pressure by allowing coolant to beexchanged across a valve, active degas systems control pressure byallowing air to be exchanged across a valve. In degas systems, coolantthermal expansion causes fluid to flow into the degas bottle, therebyincreasing air pressure within the degas bottle. When the air pressurewithin the bottle exceeds an upper threshold pressure, for example 21psi, the pressure opens a valve allowing air to escape. In one example,this valve may be located in the fill cap of the reservoir (e.g., degasbottle cap 304 at FIG. 3). If air has been released from the system, thenext time the system cools back to ambient temperatures, the pressure inthe degas bottle will be below atmospheric pressure. In this condition,another valve located in the fill cap will open to allow ambient air tore-enter the degas bottle. The degas bottle is given its name due to thefact that it separates air that is entrained in the coolant. Somecoolant from various local high points in the cooling system is allowedto flow through vent tubes back to the degas bottle.

Cooling system 200 may further include a turbocharger 206. Coolant maycirculate from water outlet 204, through turbocharger 206, and towarddegas bottle outlet hose 219 via turbo outlet hose 218. Turbo outlethose 218 may be connected to degas bottle outlet hose 219 downstream ofthe connection between lower level sensor hose 216 and degas bottleoutlet hose 219. In this way, high-temperature coolant and/or vaporcarried by turbo outlet hose 218 may not affect fluid transfer betweendegas bottle 208 and vertical standpipe 210.

One or more temperature sensors may be coupled to the cooling system, atthe engine hot water outlet, to estimate a coolant temperature. Forexample, coolant temperature may be estimated by an engine coolanttemperature (ECT) sensor positioned to be in contact with the heatedcoolant. Alternatively, coolant temperature may be estimated by acylinder head temperature (CHT) sensor positioned on the engine block,for example, positioned a few millimeters of aluminum away from theflowing engine coolant in the cylinder head. Coolant temperature mayalso be estimated within vertical standpipe 210, and a circuit boardtemperature may be estimated within the circuit board of coolant levelsensor 212, as further described in reference to FIG. 7.

As elaborated herein, the vertical standpipe may be fluidically coupledto the coolant overflow reservoir such that a level of coolant in thereservoir equilibrates with the level of coolant in the verticalstandpipe. Consequently, a controller may be configured to infer thelevel of coolant in the degas bottle based on the level of coolant inthe vertical standpipe. This enables accurate coolant level estimationwithout incurring issues associated with the use of a level sensor inthe degas bottle. Further, the coolant level in the vertical standpipemay be used to adjust engine operation so as to reduce engineoverheating resulting from low coolant levels in the degas bottle.

FIG. 3 provides one view of the positioning of the vertical standpiperelative to the degas bottle and vehicle frame. Vertical standpipe,indicated generally at 310, is affixed to frame 302 via severalcomponents within standpipe mounting support 320, as described infurther detail with reference to FIGS. 4, 5, 6 and 7. Vertical standpipe310 may be further affixed to frame 302 via lower standpipe mountingsupports 321 a and 321 b. The position of vertical standpipe 310 withinthe underhood environment is based on several criteria, including butnot limited to ensuring space for routing upper level sensor hose 314and lower level sensor hose 316 between vertical standpipe 310 and degasbottle 308 and mounting the standpipe to a strong and rigid support inorder to avoid damaging vibrations. Additionally, the distance betweenthe standpipe and the degas bottle is minimized to reduce the effect ofvehicle acceleration and attitude on the difference in the standpipefluid level and the degas bottle fluid level. In this preferredembodiment, the standpipe is be aligned with the lateral centerline ofthe degas bottle, thereby minimizing the influence of lateralacceleration and side-hill attitudes on the difference in fluid levelsbetween the standpipe and degas bottle. As depicted in FIG. 3, thelateral direction is in and out of the page. Furthermore, thelongitudinal distance (from left to right in FIG. 3) between the degasbottle and the vertical standpipe may be such that longitudinalacceleration and uphill/downhill attitudes provide fluctuations in thevertical standpipe fluid level, thereby providing the ability to confirmcontinuous sensor function.

Vertical standpipe mounting supports 320, 321 may be included as part ofstandpipe wall 382. Alternatively, the standpipe may be attached tostandpipe wall 382 via one or more of a bolt, weld, etc. Verticalstandpipe 310 is affixed such that its major axis is aligned with thegravitational force when the vehicle is at rest on a level plane.Vertical standpipe 310 and degas bottle 308 have a fixed relativepositioning. The orientation of vertical standpipe 310 is configuredsuch that the major axis of vertical standpipe is parallel to thevertical axis of degas bottle. That is to say, vertical standpipe 310and degas bottle 308 may be configured to have a common level plane attheir top surfaces. However, a bottom surface of the vertical standpipemay be arranged to be positioned lower than the bottom surface of thedegas bottle. This particular configuration may ensure that a minimumthreshold level coolant is present in the standpipe even when thecoolant level in the degas bottle is close to empty. Such aconfiguration may be utilized because ultrasonic level sensors cannotmeasure below a minimum level. If the sensor is placed such that itsminimum level is below the degas bottle outlet, any coolant in the degasbottle will be within the measurement range of the sensor. As such, therisk of the degas bottle running empty and causing engine overheating isreduced. In this way, a coolant level may be defined by a commonhorizontal plane cutting across both degas bottle 308 and verticalstandpipe 310 when the vehicle is at rest on a level plane (as furtherdescribed with reference to FIG. 4).

Vertical standpipe 310 may include a standpipe cap 312, an ultrasoniclevel sensor for measuring a coolant level (not pictured), and sensorhousing 360. Vertical standpipe 310 is fluidly coupled to degas bottle308 via upper level sensor hose 314 and lower level sensor hose 316.Specifically, upper level sensor hose 314 is positioned to allow air toflow between the top of vertical standpipe 310 and the top of degasbottle 308, and lower level sensor hose 316 is positioned to allowcoolant to flow between the bottom of vertical standpipe 310 and thebottom of degas bottle 308. In this way, the fluid level betweenvertical standpipe 310 and degas bottle 308 may reach an equilibriumlevel when the vehicle is at rest, facilitating a comparison of acoolant level within the vertical standpipe and a coolant level in thedegas bottle.

Degas bottle 308 includes degas bottle cap 304, degas inlet hose 306,and degas outlet hose 319 in addition to upper level sensor hose 314.Degas bottle 308 may comprise an upper piece 311 and a lower piece 313.In alternate embodiments, degas bottle 308 may comprise a single pieceor more than two pieces. Degas bottle 308 may be affixed to any suitablyhigh and rigid structure in such a way that degas bottle 308 issubstantially level. Being substantially level includes being at anattitude wherein the top surface extends along a plane that issubstantially perpendicular to the direction of gravity, for examplewithin 5 degrees of perpendicular along each axis of extension. As oneexample, degas bottle 308 may be affixed to the inner fender via degasbottle mounting support 309. In one example, degas bottle mountingsupport 309 may be included as part of lower degas bottle piece 313. Inother examples, degas bottle mounting support 309 may be attached tolower degas bottle piece 313 via a fastening mechanism. In furtherexamples, degas bottle mounting support 309 may instead be attached toor be included as part of upper degas bottle piece 311. When affixed todegas bottle 308, degas bottle cap 304 may prevent coolant in thecoolant reservoir from evaporating and escaping into the atmosphere.When degas bottle cap 304 is removed from degas bottle 308, an openingon the top of degas bottle 308 for supplying more coolant to the systemmay be exposed. Coolant may also be introduced into degas bottle 308from other cooling system components via degas bottle inlet hose 306.For example, the inlet hose may direct coolant into the degas bottlefrom the radiator. In some examples, degas bottle cap 304 may include avalve, such as a pressure relief valve or a spring activated valve. Whenthe fluid in the radiator heats up, such as due to extensive engineheating, the coolant expands, causing the pressure in the cooling systemto increase. The cooling system pressure may escape via degas bottlefill cap 304. Specifically, the maximum pressure in the degas bottle maybe determined via a spring-loaded valve in degas bottle fill cap 304.When the pressure reaches a threshold, such as 21 psi, the pressurepushes open the valve in degas bottle fill cap 304, allowing pressurizedair to escape from the degas bottle to the underhood environment. Whenthe system cools back down, a vacuum is created that draws air back infrom the underhood environment via another valve in degas bottle fillcap 304.

FIG. 4 provides an alternative view of part of a cooling system, andfurther details the fluidic coupling of degas bottle 308 and verticalstandpipe 310. A sensor 340 may be affixed to the bottom of degas bottle308 to measure fluid levels in the degas bottle directly. Sensor 340 maybe positioned within sensor housing 342. Sensor 340 may be connected tothe electronic control system, and enabled to communicate withcontroller 12 via the controller area network (not shown).

Lower level sensor hose 316 is coupled to degas bottle outlet hose 319via T-joint 332. T-joint 332 is oriented so that the 90-degree branchingfrom outlet hose 319 is downward such that any entrained bubbles in hose319 tend to bypass hose 316. Further, when coolant is absent from degasbottle 308 and degas bottle outlet hose 319, a volume of coolant mayremain “trapped” in lower level sensor hose 314 and vertical standpipe310. This trapped volume of coolant may be measurable by ultrasoniclevel sensor 362. Additionally, a connection may be made between a turbooutlet hose (218 at FIG. 2) and degas bottle outlet hose 319 downstreamof T-joint 332 (obscured at FIG. 4 by vertical standpipe 310). Thisconnection may be made by a second T-joint 334 oriented so that the90-degree branching from degas bottle outlet hose 319 is upward,anti-parallel to the branching of T-joint 332. In this way, hot and/orvaporized coolant generated by return flow from turbo outlet hose 218(the return flow varying as a function of engine speed), may not affectthe difference in coolant level between degas bottle 308 and verticalstandpipe 310. Lower level sensor hose 316 may be further coupled to theside of vertical standpipe 310, at a level below a blanking distanceassociated with ultrasonic level sensor 362 (as further discussed belowin reference to FIGS. 7 and 11).

Vertical standpipe 310 is positioned such that the bottom of standpipe310 is below the bottom of degas bottle 308 and below T-joint 332. As aresult, if the coolant level in degas bottle 308 approaches the bottomof the bottle or falls below the bottom of the bottle, the correspondinglocal coolant level in standpipe 310 may remain at a specified levelsubstantially above ultrasonic level sensor (ULS) 362. The specifiedlevel may be based on the level of a horizontal plane extending from thetop of T-joint 332. In this way, if the local coolant level in thestandpipe is estimated to be zero, a degradation of the coolant systemsuch as a disconnected hose may be indicated, and if the local coolantlevel in the standpipe is estimated to be within a threshold distance ofthe specified level, an empty degas bottle may be indicated.

As shown in FIG. 4, vertical standpipe 310 is affixed to frame 302 insuch a way that the top of the vertical standpipe occupies the samehorizontal plane as the top of degas bottle 308. Vertical standpipe 310has a larger vertical extent than degas bottle 308, and consequently thebottom of vertical standpipe 310 is below the bottom of degas bottle308. As such, when degas bottle 308 is empty, a level of coolant mayremain in vertical standpipe 310, providing a medium interface off ofwhich ultrasonic pulses from ULS 362 may reflect. At fluid equilibrium,the local coolant level in vertical standpipe 310 that corresponds to anempty degas bottle may be defined by a horizontal plane extending thetop of T-joint 332, as depicted by coolant level line 333 at FIG. 4. Inthis way, a specified level measurement in vertical standpipe 310 may beassociated with an empty bulk coolant level in degas bottle 308,allowing for an empty bulk coolant level measurement to bedifferentiated from a condition such as a disconnected hose, which mayinduce an empty local coolant level in vertical standpipe 310.

Vertical standpipe 310 may be equipped with standpipe cap 312. Standpipecap 312 may be configured to fit in the top of vertical standpipe 310such that the major axis of standpipe cap 312 is parallel to the majoraxis of vertical standpipe 312. Standpipe cap 312 may have a smoothsurface 380, which may aid in the reflection of sound waves such asthose emitted by ultrasonic level sensor 362. In one example, standpipecap 312 may be manufactured via a spin welding technique. Verticalstandpipe 310 may be a cylindrical shell with a sufficiently smallhorizontal cross section in order to serve as a waveguide for ultrasonicsound waves. As a non-limiting example, the horizontal cross section ofvertical standpipe 310 may be approximately 17.25 millimeters indiameter, and slightly larger than the sensing element of the ultrasoniclevel sensor. Vertical standpipe wall 382 may be composed of a smooth,rigid plastic, for example a PA66 material with 30% glass fill.

Ultrasonic level sensor (ULS) 362 may be a piezoelectric transducerelement capable of both sending and receiving ultrasonic pulse signals.ULS 362 may be affixed to the bottom of vertical standpipe 310 firmlywithin sensor housing 360, and configured to emit sound pulses upwardthrough the cavity of the pipe. ULS 362 may be electronically connectedto ULS circuit board 364. ULS circuit board 364 may physically extendbeyond the extent of ULS 362 and be in electronic communication with anengine controller (e.g., 12 of FIGS. 1-2). In a non-limiting example,sensor 340 may also be an ultrasonic level sensor configured to makedirect estimates of coolant level in degas bottle 308. Sensor housing360 may be sealed to upper standpipe wall 382 with an o-ring andretained with a metal spring clip 336 to allow quick assembly of the twohalves of the standpipe wall. Sensor housing 360 may be made of amaterial with a coefficient of thermal expansion closer to that of ULS362 when compared to that of upper standpipe 382, for example PPS GF30.Lower standpipe cover 368 may be attached to the bottom of sensorhousing 360, protecting any sensor components from the environment. Thecavity surrounding circuit board 364 and ULS 362 may be filled withflexible potting compound to further enhance environmental isolation.

Continuing at FIG. 5, a bird's-eye view depicting the relativepositioning of degas bottle 308, vertical standpipe 310, and frame 302is provided. Degas bottle mounting support, shown here as attached tolower degas bottle piece 313, may include a hole with several teeth toallow sufficient compliance for assembly while maintaining aninterference fit after assembly. Upper level sensor hose 314 is shownextending horizontally between upper degas bottle piece 311 and the topof vertical standpipe 310.

As shown, vertical standpipe 310 may include an upper mounting support320 extending horizontally over frame 302 and one or more lower mountingsupports (not shown) extending horizontally below frame 302, whilevertical standpipe is affixed alongside a vertical face of frame 302.Standpipe mounting fastener 322 is shown extending vertically fromwithin upper mounting support 320 and through frame 302, restrictingmovement of vertical standpipe 310. Standpipe mounting fastener 322 mayextend through metal load limiter 324 above frame 302, thereby avoidinga joint clamp load reduction which may occur over time due to creep inupper mounting support 320.

Spring retaining clip 336, located on the upper part of verticalstandpipe 310, may be configured to provide robust retention and allowquick assembly of the two halves of vertical standpipe 310. Lowerstandpipe cover 368 is shown affixed to the bottom of vertical standpipe310, and may shield ULS 362 and ULS circuit board 364 from theenvironment. As depicted herein, lower level sensor hose 316 is coupledto vertical standpipe 310 below spring retaining clip 336 and abovelower standpipe cover 368.

Turning now to FIG. 6, the mounting of vertical standpipe 310 to frame302 is depicted in greater detail. Frame 302 includes severalcross-shaped support structures 303 between an upper face and a lowerface of the frame. Within a cavity of one of the cross-shaped supportstructures 303, a mounting wedge 326 may be inserted to aid withmounting vertical standpipe 310 to frame 302. Mounting wedge 326 may beconstructed to fit within an inner lattice of the cross-shaped supportstructure. For example, where the inner lattice has a substantiallytriangular shape, the mounting wedge may also be configured to have amatching triangular shape such that a snug fit is achieved. The top ofmounting wedge 326 may be in direct contact with the bottom of an upperface of frame 302. Standpipe mounting fastener 322 may extend verticallyfrom above frame 302, through metal load limiter 324, through standpipemounting support 320, through a cavity in frame 302, and through acavity in mounting wedge 326. Standpipe mounting fastener 322 may becoupled to mounting wedge 368 via J-clip 328. In this way, by couplingstandpipe mounting support 320 to mounting wedge 326 housed within across-shaped support structure 303, stability of the position ofvertical standpipe 310 in relation to frame 302 may be improved.

As shown, vertical standpipe 310 may extend substantially below thesection of frame 302 to which it is affixed. Sensor housing 360 mayextend horizontally, beneath frame 302, from vertical standpipe 310.Sensor housing 360 may be include a cavity to accept lower level sensorhose 316, and may include an electrical connection to controller 12.

FIG. 7 provides a cross-sectional view of vertical standpipe 310, theconfiguration of ULS 362 and sensor housing 360, and the configurationof the upper mounting structure including mounting support 320 andmounting fastener 322. Vertical standpipe 310 is configured to couple toupper level sensor hose 314 along standpipe wall 382 adjacent tostandpipe cap 312. Vertical standpipe 310 is further configured tocouple to lower level sensor hose 316 just above ULS circuit board 364.

Mounting support 320 may be included as part of vertical standpipe wall382, as shown. Mounting fastener 322 may be oriented perpendicularly tothe bottom face of mounting support 320 and the top face of mountingwedge 326. Mounting fastener 322 may be a suitable fastening mechanismsuch as a bolt or screw.

Turning to the lower section of vertical standpipe 310, ULS circuitboard 364 is shown electrically connected to ULS 362, coolanttemperature sensor 367 (shown in FIG. 4), and circuit board temperaturesensor 369. Coolant temperature sensor 367 may be positioned above ULScircuit board 364, and ULS circuit board temperature sensor 369 may bepositioned below ULS circuit board 364. Temperature sensors 367 and 369may be configured to periodically or continuously estimate temperaturesof coolant within vertical standpipe 310 and of ULS circuit board 364,respectively. In one example, ULS circuit board temperature sensor 369may be a surface-mounted thermistor affixed to the surface of ULScircuit board 364.

Ultrasonic level sensor 362 is configured to periodically produce soundwaves for developing usable sensor data. In some embodiments ULS 362 maybe configured to produce a set of multiple ultrasonic pulses (e.g., fivepulses), spaced far enough apart that the pulses have enough time totravel the length of the standpipe and return to the sensor (based onlength and speed of sound in fluid) before another pulse is sent out(e.g., 5-8 milliseconds between pulses), and produce a set periodicallyevery total time of pulses seconds (e.g., every 100 milliseconds). ULS362 may produce these sound signals continuously during conditions wherethe ignition state is in an engine running mode. ULS 362 is asend/receive device, and accordingly is configured to receive soundwaves. When ULS 362 is placed in vertical standpipe 310 and fluid ispresent in the standpipe, pulses produced by ULS 362 will be reflectedby a fluid-air interface or by a vertical standpipe cap 312 and travelback toward ULS 362. If the energy of the returning pulse is above alower threshold energy, the returning pulse will transmit a portion ofits energy and may be received by ULS 362. The term first-order echo mayherein also be used to refer to this returning pulse. Further, the termecho may herein refer to this returning pulse unless specifiedotherwise. In some sensors, the returning pulses will reflect on thebottom of the fluid cavity and travel to the fluid-air interface andreflect a second time. These waves will then travel back down toward ULS362. This second harmonic return, herein also referred to as asecond-order echo, may also be detected and can be used for signalverification and more complex operation.

Ultrasonic level sensor circuit board 364 may include memory withinstructions to adjust a power level supplied to ULS 362 based on theenergy associated with ultrasonic pulse signals received by ULS 362. Forexample, as described in further detail with reference to FIG. 10, whenthe energy associated with a set of ultrasonic pulse signals is greaterthan an upper threshold or when the number of second-order echoesassociated with a set of pulses is greater than a threshold number, ULScircuit board 364 may be controlled (e.g., by engine controller 12 atFIG. 1) to decrease the power supplied to ULS 362 for emittingultrasonic pulses. As another example, when the energy associated with aset of ultrasonic pulse signals is less than a lower threshold, ULScircuit board 364 may be controlled (e.g., by engine controller 12 atFIG. 1) may increase the power supplied to ULS 362 for emittingultrasonic pulses. The pulse energy being less than a lower thresholdmay include no ultrasonic pulse being detected when a pulse is expectedto be detected. ULS circuit board 364 is configured to measure time, andmay include programs in memory configured to capture timestamps ofultrasonic pulses received by ULS 362. ULS circuit board 364 is furtherconfigured to estimate temperatures of the assembly and fluid viatemperature sensors 367 and 369, respectively (e.g., via thermistorvoltage measurements from sensors 367 and 369). In this way, ULS circuitboard 364 may produce improved estimates of a standpipe coolant levelbased on ultrasonic pulse times and temperature estimates. ULS circuitboard 364 may be configured to transmit data to controller 12 via a CANbus, including but not limited to temperature estimates from sensors 367and 369, ultrasonic pulse timestamps, ultrasonic pulse energy levels,and sensor-processed standpipe coolant level estimates (as furtherdescribed with reference to FIG. 11).

ULS 362 may be further configured to broadcast information to an enginecontroller (such as controller 12 of FIG. 1) via a controller areanetwork, as indicated. In one example, ULS 362 may be a one-way orbroadcast-only device on the CAN.

FIG. 8 depicts a detailed view of standpipe cap 312. Standpipe cap 312may be manufactured via spin-welding. Standpipe cap 312 may becylindrical and include a circumferential groove 384 configured toaccept and rest on the top of vertical standpipe wall 382. Standpipe capsurface 380 may be within the area encompassed by circumferential groove384. Standpipe cap surface 380 may be constructed to be smooth, flat,and parallel to the emitting surface of ULS 362. In this way, standpipecap surface 380 may efficiently reflect sound waves emitted from the ULSat the bottom of the standpipe. By improving the efficiency of soundreflection, the accuracy of fluid level estimation in the verticalstandpipe is increased when the standpipe is full of fluid. If capsurface 380 were rough or angled with respect to ULS 362, reflectedsound may be scattered away from ULS 362 such that the standpipe wouldappear empty. As such, this improves the reliability of coolant levelestimation in the degas bottle.

FIG. 9 provides a high-level routine 900 for determining a bulk coolantlevel in a degas bottle based on a level sensor reading in a fluidlycoupled vertical standpipe, such as degas bottle 308 and verticalstandpipe 310. The routine further depicts the adjusting of engineparameters based on the bulk coolant level. Routine 900 may be executedcontinuously throughout engine operation to ensure that there is asufficient level of coolant in the coolant system to prevent overheatingof any engine components. Each iteration of routine 900 may be hereinreferred to as a measurement period. The routine consists of estimatinga coolant level in the vertical standpipe based on data from theultrasonic level sensor, adjusting the estimate of the coolant level inthe vertical standpipe based on slosh parameters such as vehicleacceleration, vehicle attitude, and previous coolant levels to determinea current coolant level in the degas bottle, adjusting a long-term bulkcoolant level based on the estimate of the current level in the degasbottle, and adjusting engine operating parameters based on the long-termbulk coolant level.

Routine 900 begins at 902, where an ultrasonic level sensor mayperiodically emit a set of ultrasonic pulses upward from the bottom ofthe vertical standpipe. For example, as described above, a ULS may emita set of 5 sequential ultrasonic pulses of a specified energy, eachpulse spaced 5-8 milliseconds apart. The energy of the emitted pulsesmay be determined based on several factors including feedback from theenergy of previously-received pulses. Specifically, the energy of thepulses may be increased if previous returning pulses were below athreshold amount of energy, or were not detected, and may be decreasedif more than a threshold number of second and/or third-order harmonicechoes were detected. The time interval between each pulse set may bedetermined based on the expected values of the fluid's speed of soundand total length of standpipe to be measured, such that the time betweenis at least longer than the period of the first harmonic of thepipe/fluid. For example, the ULS may emit a set of pulses every 100milliseconds.

Once an ultrasonic pulse is emitted from the ULS, it may travel upwardthrough the coolant in the standpipe until reaching a medium interface,such as a coolant-air interface, or an air-solid interface if thestandpipe has no coolant in it. Some of the energy associated with theultrasonic pulse may be reflected at the interface, creating an echopulse, and the rest of the energy associated with the ultrasonic pulsemay transmit or refract through the interface, or dissipate in someother way. The echo pulse may travel back toward the ultrasonic levelsensor, and at 904, may be detected by the ultrasonic sensor. This echomay be referred to as a first-order echo. In some examples, an echopulse may be at or below a lower threshold energy, and as such may beundetectable by the sensor. In further examples, the echo received bythe ultrasonic level sensor may be a second echo associated with anemitted pulse. Each echo that is detected may be assigned a timestamp,as described in further detail below.

When multiple successive echoes are returned with sufficient energy, theassociated timestamps may be compared for the primary, secondary andtertiary echoes in comparison to one another and in comparison tomultiples for the primary echo. These echoes correlate with the expectedharmonic response. These timestamps are provided with sufficient timeresolution for proper signal analysis, and indicate the amount of timeelapsed between the emission and reception of said echo. This timestampmay herein also be referred to as an echo time. In some examples, atimestamp may only be assigned to pulses with an energy at or above alower threshold energy. If a single ULS is configured to both send andreceive signals within the standpipe, the sensor may be configured toignore received pulses for a threshold duration after the emittedexcitation is stopped. This threshold duration may herein be referred toas a “blanking time” which correlates to a potential reflection that canoccur at the bottom of the fluid interface and give a false indicationof low fluid level. The blanking time may be determined based on avariety of factors such as the sensor housing materials used, couplingmaterials assisting to transmit from the transducer to the housing, andother geometric features present in the standpipe. The internal computeror processor of the ULS circuit board may also designate echoes as beingfirst-order echoes or higher-order echoes such as second-order echoes.

At 906, the internal computer of the ULS may determine an echo time foreach received pulse. Based on these echo times, the ULS computer mayalso determine an internal estimate for the local coolant level in thestandpipe. The internal coolant height estimate may be based on anestimated speed of sound in coolant, including a temperaturecompensation factor and an echo time. A coolant level may be estimatedfor each received first-order echo in a measurement period. An averageof the coolant levels in a given measurement period may be determined toreach a final sensor-processed local coolant level in the verticalstandpipe. A comparison is made between these signals to ensure thesignal is a true detection of the fluid level. During conditions whereinexcessive fluid churning or intra-pulse fluid-air movement could beconfused with less accurate readings, more complex statisticaldeterminations than an arithmetic mean may be necessary to analyze thetimestamps of the first-order echoes. Thus, determining an average mayconsist of one or more of determining a mean, mode, median, weightedaverage, other statistical function, and a standard deviation, and thenprocessing the coolant levels using an appropriate mean or median basedon data sample outliers. For example, when the primary echo times withinthe set of pulses are all within 1 microsecond of one another, a highquality signal may be indicated. However, when one primary echo time issignificantly different than the other, a lower level of confidence maybe indicated.

At 908, an amount of power supplied to the ULS for pulse emission may beadjusted based on one or more of the energies and number of first andsecond echo times pulses for the current measurement period. In oneexample, routine 1000 (at FIG. 10) may be executed to adjust the supplyof power. Adjusting the power supplied to the ULS for pulse emission mayinclude selectively increasing the power when a first threshold numberof received pulses are below a lower threshold energy, and selectivelydecreasing the power when a second threshold number of higher-orderechoes are received in the measurement period. The threshold number ofreceived pulses may be based on the presence of any primary echo data(e.g., the threshold number may be the size of the pulse set) while thethreshold number of higher-order echoes may be based on the second orderecho times available. Adjusting the power supplied to the ULS is furtherdescribed below with reference to FIG. 10.

The ULS may broadcast information associated with the emitted andreceived pulses of the current measurement period to the enginecontroller (such as controller 12) at 910. For example, the ULS maybroadcast a number of received echoes above the lower threshold energy,a sensor-processed local coolant level estimate, timestamps for firstand second-order echoes of each emitted pulse in the measurement period,and sensor circuit and standpipe coolant temperature estimates. The ULScircuit board temperature and standpipe coolant temperature estimatesmay be determined via sensors 367 and 369, respectively. The enginecontroller may then determine a coolant level in the vertical pipe basedon this information. The coolant level in the vertical pipe may hereinbe referred to as a local coolant level or a local level. Determining alocal coolant level may include applying the sensor-processed localcoolant level estimate as the local coolant level estimate, oralternatively may include calculating a level based on echo times, ablanking distance, and the physical extent of the standpipe. Determininga local coolant level is described in further detail with reference toFIG. 11.

The coolant level in the standpipe may not correspond directly to thecoolant level in the degas bottle, the latter level herein also referredto as the bulk coolant level or bulk level. For example, if the vehicleis accelerating or decelerating, or is at an attitude, the local coolantlevel may diverge from the bulk coolant level due to slosh. Toaccommodate for the divergence of the bulk level from the local leveldue to slosh, a compensation term may be calculated by the enginecontroller. This compensation term may be used to adjust the localcoolant level estimate to a bulk coolant level estimate at 914, forexample via routine 1400 at FIG. 14. The compensation term may be basedon motion parameters of the vehicle, for example based on one or more oflongitudinal attitude and acceleration, lateral attitude andacceleration. Applying compensation to the local coolant level estimateto adjust for slosh is described in further detail in reference to FIG.14.

After an adjusted local coolant level estimate has been determined forthe measurement period at 914, routine 900 proceeds to 916, where thebulk coolant level estimate may be adjusted based on the adjusted localcoolant level estimate. Adjusting the bulk coolant level estimate mayinvolve filtering the adjusted local coolant level estimate into thebulk coolant level estimate. Adjusting the bulk coolant level estimateis described in further detail below, in reference to FIGS. 14 and 16.The bulk coolant level estimate may not be adjusted during measurementperiods in which a local coolant level estimate is not determined. Abulk coolant level estimate may correspond with one or more bulk coolantstates, the bulk coolant states defined by one or more level thresholds.

Routine 900 then proceeds to 918, where the coolant state of the vehiclemay be adjusted based on the bulk coolant level estimate. The vehiclemay have a fixed number of possible coolant states, for instance, EMPTY,LOW, OK, FAULTED, and UNKNOWN/DEGRADED. Coolant states may corresponddirectly to a bulk coolant level, or may indicate degradation ofhardware components such as an ultrasonic level sensor. In some cases,adjusting the coolant state may occur only a coolant level indicating anew coolant state has persisted for a threshold duration.

Based on the coolant state, engine operating parameters may be adjustedat 920. For example, when the coolant level is below a lower thresholdfor more than a threshold duration and vehicle operating parameterssuggest a proper coolant level can be detected, a low coolant state maybe assumed. This may result in limiting operation where engine loads maybe restricted to be below an upper threshold to ensure that enginecomponents will maintain intended operation. In another example, if thecoolant state is LOW, the controller may display a message to the engineoperator indicating a low coolant level. Adjusting the coolant state isdescribed in further detail with reference to FIG. 18. In some cases,system diagnostics may be executed based on coolant state at 922, forinstance, sensor degradation may be determined based on the coolantstate and change in coolant state over a duration of vehicle operation.Routine 900 then terminates.

FIG. 10 depicts a routine 1000 for adjusting the power supplied to theultrasonic level sensor for pulse emission based on feedback from theenergy of received pulses. The power supplied to the ultrasonic levelsensor for pulse emission may herein also be referred to as the transmitenergy. Routine 1000 may be executed during each measurement period,after the set of pulses has been received, and may increase the energyefficiency of the ultrasonic level sensor.

Routine 1000 begins at 1002, where the number of first-order echoeswithin the measurement set with an amount of energy above a lowerthreshold is determined and compared to a threshold number. The lowerenergy threshold may be determined based a fixed minimum value]. Thisminimum threshold number may be determined based on providing sufficientfunction under most steady state operation conditions. For example, if 5pulses were emitted for the measurement period, a threshold number maybe 4 pulses out of 5 having an amount of energy above the lowerthreshold. If the number of echoes with sufficient energy is higher thana threshold, it may be determined that the energy output of the sensoris sufficiently high. In addition, it may be determined that furtheroptimization of the energy output may be possible. In particular, if theenergy output is sufficiently high then the energy output of the sensormay be reduced without incurring a substantial drop in the number ofechoes with sufficient energy. By reducing the energy output withoutaffecting echo efficiency, power reduction benefits can be achieved.Additionally, when operating with high pulse emission energies,unexpected additional pulses may be detected due to improperly reflectedenergy that result in false data being provided to the measurementsystem. Thus, it is beneficial to provide reduced ultrasonic energywhenever conditions allow.

In one example, in response to a low enough number of valid firstharmonic echoes (e.g., 0 or 1) being received, energy output level maybe increased to attempt to get enough energy quickly to regainsufficient 1^(st)/2^(nd) order returns (e.g., a 10%-20% increase). Inanother example, when all of the first order harmonics are present andmore than a high number of second harmonics are validly returned (e.g.,more than 4 or 5 second harmonics), the amount of pulse energy broadcastis reduced by a small decrement amount (e.g., a 1% decrease). In otherexamples, some conditions may indicate maintaining the current transmitenergy when all the transmitted pulses are providing clear first andsecond echo times.

Accordingly, if the number of echoes with an amount of energy above thelower energy threshold is at or above the threshold number, routine 1000proceeds to 1004, where the energy supplied to the ULS for emittingpulses may be decreased. Otherwise, if the number of echoes with anamount of energy above the lower threshold is below the thresholdnumber, routine 1000 proceeds to 1006, where the energy supplied to theULS for emitting pulses may be increased. Herein, based on the number ofechoes with sufficient energy been lower than the threshold, it may bedetermined that the energy output of the sensor is not high enough. Inaddition, it may be determined that further optimization of the energyoutput is necessary. Accordingly, to improve the number of echoes thathave sufficient energy, the energy output of the ULS is increased.

Decreasing transmit energy at 1004 may include, under a first set ofconditions, decreasing the transmit energy at a first rate, and under asecond set of conditions, decreasing the transmit energy at a secondrate, the second rate less rapid than the first rate. For example, thefirst set of conditions may include receiving a threshold numberfirst-order echoes above the lower energy threshold, while alsoreceiving a number of higher-order pulses above an upper thresholdnumber. In this example, the transmit energy may be decreased at a firstslow rate, the rate intended to ensure a continuity of the signalscoming back and having a controlled reduction of power. An excessivereduction rate may result in a dithering of sufficient and insufficientdata in alternating cycles. This dithering behavior may then be falselydetected a loss of proper signal function resulting in unnecessaryvehicle response conditions. The second set of conditions may includeevery first-order echo in the measurement period being above the lowerthreshold energy, and a number of higher-order pulses below the upperthreshold number. In this example, the transmit energy may be decreasedat a second slow rate, the second rate slower than the first. In anotherexample, the first set of conditions may include the transmit energybeing at the physical maximum level and the number of first-order echoesabove the lower threshold energy is above the threshold number. Incomparison, the second set of conditions may include the transmit energybeing at the physical maximum level and the number of first-order echoesabove the lower threshold energy being below the threshold number.

Increasing the transmit energy at 1006 may include, under a first set ofconditions, increasing the transmit energy at a first rate, under asecond set of conditions, increasing the transmit energy at a secondrate, the second rate less rapid than the first rate. In some examples,under a third set of conditions, the transmit energy may be jumped tothe physical maximum level and maintained at the physical maximum leveluntil these conditions are no longer detected. For example, the firstset of conditions may include the number of first-order echoes with anamount of energy above the lower energy threshold being below a lowernumber threshold but non-zero. In this example, the transmit energy maybe increased at a faster rate, the rate determined based on the numberof valid first order pulse returns lower than a threshold (e.g., thethreshold may be 3 pulses). The second set of conditions may includehaving a low number of second order harmonic pulse returns (e.g., lessthan 3), in which case the transmit energy may be increased at a lowerrate, the rate determined based on the balance of valid first and secondharmonic pulse returns. The third set of conditions may include thenumber of first-order echoes with an amount of energy above the lowerenergy threshold being zero. In this example, the transmit energy may beincreased to a maximum level. In some examples, if one of the first orsecond set of conditions is detected but the transmit energy is at anupper threshold, the upper threshold below the maximum level, thetransmit energy may be maintained and not increased. In another example,transmit energy may be maintained when one of the first or second set ofconditions is detected but the transmit energy is above the upperthreshold and below the maximum level.

FIG. 11 provides an example routine 1100 for estimating the localcoolant level in the standpipe based on information from the ultrasoniclevel sensor and engine operating conditions, and adjusting thisestimate with a compensation term. During a first set of conditions, alocal coolant level estimate may be calculated based on asensor-processed level estimate, and during a second set of conditions,the controller may calculate a level estimate based on one or more ofthe first-order echo time stamps, estimates of coolant and ULS circuittemperatures, an estimated coolant blend, vehicle acceleration andattitude measurements, and physical parameters of the standpipe. Routine1100 may be executed during each measurement period.

At 1102, the controller receives raw data from the ultrasonic levelsensor, including but not limited to a number of echoes above a lowerthreshold energy at 1104, echo timestamps 1106 for both first-order andhigher-order echoes, and coolant temperature and ULS circuit boardtemperature estimates 1110, in addition to receiving a sensor-processedcoolant level estimate 1108. At 1112, the engine may determine whetherengine conditions are quiescent, and if they are, may apply thesensor-processed coolant level estimate 1108 as the raw fluid level inthe standpipe at 1114. Determining whether engine conditions arequiescent may include determining whether one or more of dynamicacceleration of the vehicle, grade/pitch of the vehicle, and/or enginespeed change by more than threshold amounts. These parameters may bedetermined based on information from vehicle accelerometers (e.g., fromroll-stability or air bag modules) as well as engine operatingparameters from a powertrain/engine control module.

If engine conditions are not determined to be quiescent at 1112, thecontroller may proceed to calculate a local coolant level based on echotimes 1106 and temperatures 1110. At 1116, the controller checks thenumber of received first-order echoes that are at or above a thresholdamount of energy. In some cases, the threshold amount of energy may bethe energy level at which signal can be distinguished from noise. If thenumber of first-order echoes at or above the threshold amount of energyis above a threshold number of echoes, routine 1100 proceeds to 1124 tocalculate a coolant level based on these first-order echo times. Thethreshold number of echoes may be determined based on data collected forbaseline fraction of valid first harmonic echoes seen on flat ground,idle, stationary conditions. For example, if the measuring periodcomprises 5 emitted pulses, the threshold may be 4.

In some examples, a first-order echo may have been misidentified by theinternal processor of the ULS circuit board as being a higher-orderecho. Accordingly, at 1118, the controller may check the higher-orderecho timestamps and determine whether one or more first-order echoeshave been misidentified by the sensor as higher-order echoes.Determining whether a first-order echo has been misidentified may bebased on comparing the return timestamps of reported first order echoesto the calculated 2^(nd) or 3^(rd) order times that could occur(calculated based on the speed of sound and 4 standpipe lengths (2^(nd)order) or 6 standpipe lengths (3^(rd) order)). If no first-order echoeswere misidentified, then the number of first-order echoes is still belowthe threshold number. In this case, the controller may flag an invalidreading for the measurement period at 1128 because there are not enoughdata points to make a reliable estimate of the coolant level in thestandpipe. Flagging an invalid measurement period also includes notupdating the bulk coolant level based on data from the currentmeasurement period at 1130, and using bulk level data from the mostrecent valid measurement period at 1132.

If it is determined at 1118 that one or more first-order echoes weremisidentified as higher-order echoes, these echoes may be reassigned asfirst-order echoes at 1120. The controller may then again check whetherthe number of first-order echoes at or above the threshold amount ofenergy is above the threshold number of echoes. If the number is stillbelow the threshold number, routine 1100 may proceed to 1128, 1130, 1132as described above. If the number is at or above the threshold number,routine 1100 continues to 1124, where a local coolant level estimate maybe determined, for example via routine 1200 at FIG. 12.

Turning briefly to FIG. 12, routine 1200 provides an example routine forcalculating a local coolant level estimate based on echo times and anumber of temperature estimates. The calculation is based on theassumption that an ultrasonic pulse travels from the sensor, toward acoolant-air medium interface, and back to the ultrasonic level sensor inthe time indicated by its respective timestamp. An estimate of thedistance travelled by the ultrasonic pulse is calculated based on theecho time and an estimate of the speed of sound in the coolant.

Routine 1200 begins at 1202, where raw first-order echo times andcoolant temperatures are received by the controller. At 1204, a coolantblend composition may be estimated based on comparing a speed of soundestimate (estimated based on an average local standpipe level on flatground) to a currently measured speed of sound. An estimate for thespeed of sound in the coolant may then be determined at 1206, based onestimated coolant and ULS circuit temperatures, as well as the estimatedcoolant blend. With an estimated speed of sound and a time stamp, adistance travelled for each pulse may be calculated at 1208 based on theformula:Distance=0.5*v_sound*t_0,where v_sound is the estimated speed of sound, t_0 is the first-orderecho time, and the product of these two is multiplied by one half toaccount for the fact that a pulse must travel twice the length of thecoolant level to return to the sensor. A distance may be estimated foreach first-order echo in the set that is above the lower thresholdenergy.

Returning to FIG. 11 at 1126, the standpipe coolant level estimates ofroutine 1200 may be compared to the physical range of the standpipe. Forexample, the memory of the controller may contain an upper thresholdvalue for a maximum level of coolant level based on the distance betweenthe ULS sensor and the top of the vertical sensor, and may contain alower threshold value for a minimum level of coolant based on thedistance between the ULS sensor and the lower level sensor hose (316 inFIG. 3). In other examples, the lower threshold value may be based onthe blanking distance of the sensor. The physical range of the standpipemay then be any level between the upper physical threshold and the lowerphysical threshold. If the local level estimates are not within thephysical range of the standpipe, routine 1100 proceeds to 1128. In someexamples, being within the physical range of the standpipe may includebeing within a threshold margin below the lower physical threshold orwithin a threshold margin above the upper physical threshold. In theseexamples, the threshold margins may be determined based on expectedworst-case part tolerances, and further based on the lower and upperphysical thresholds themselves.

However, if the estimated standpipe levels are within the physical rangeof the standpipe, routine 1100 continues to 1134, where a decision ismade based on whether the estimated standpipe levels are within thestandpipe range, or within the threshold margins outside the rawstandpipe. If the raw standpipe level is outside the standpipe range andwithin the threshold margins, the raw standpipe level is clipped to bewithin the physical range at 1136. If the raw standpipe level is withinthe physical range at 1134, clipping may not be necessary, and routine1100 may continue at 1138.

At 1138 an average of the calculated and clipped level estimates may bedetermined. Determining an average may consist of one or more ofchecking a mean, median, and a standard deviation, then processing thecoolant levels using an appropriate mean or median based on data sampleoutliers. For example, when one or more of the samples is outside of thephysical range, determining an average may include only the points thatwere measured as originally in-range. This average may be applied as theraw local coolant level estimate or raw standpipe coolant level estimatefor the measurement period. This average may then be applied as the rawstandpipe coolant level estimate at 1140. At 1142, a separate routinemay be executed to estimate the bulk coolant level based on the rawstandpipe coolant level estimate and other factors such as vehicleacceleration and attitude. For example routine 1400 at FIG. 14 may beexecuted to estimate a bulk coolant level. This process described infurther detail with reference to FIGS. 13-16.

FIGS. 13A-13C provide depictions of a coolant reservoir (degas bottle1302) fluidly coupled to a vertical standpipe 1304, and oriented atthree different angles relative to a level plane. Degas bottle 1302 isshown with degas bottle cap 1328. An upper fluidic connection isestablished between degas bottle 1302 and vertical standpipe 1304 viaupper level sensor hose 1326, and may allow a transfer of air betweenthe top of degas bottle 1302 and the top of vertical standpipe 1304.When degas bottle 1302 and vertical standpipe 1304 are level, upperlevel sensor hose 1326 may extend horizontally between the two vessels,such as illustrated in FIG. 13A. A lower fluidic connection isestablished between degas bottle 1302 and vertical standpipe 1304 vialower level sensor hose 1318, and may allow a transferring of coolant1306 between degas bottle 1302 and vertical standpipe 1304. Lower levelsensor hose is coupled to degas bottle outlet hose 1316 via a T-joint1320, oriented so that lower level sensor hose 1318 diverges from outlethose 1316 in a downward direction. Lower level sensor hose 1318 iscoupled to degas bottle outlet 1316 below the bottom of degas bottle1302, and upstream of turbo outlet 1322. Vertical standpipe 1304 mayinclude ULS 1308 for estimating a local coolant level. ULS 1308 may beconnected to a controller area network (not pictured).

By establishing a fluidic connection between a larger vessel, such asdegas bottle 1302, and a smaller, narrow vessel such as verticalstandpipe 1304, a transfer of fluid between the two vessels produces agreater effect on the coolant level of the smaller vessel than on thelarger vessel. During some conditions, local coolant level 1314 and bulkcoolant level 1312 may be the same or at least within a lower thresholdvalue of each other, such as illustrated at FIG. 13A. Conditions inwhich local coolant level 1314 and bulk coolant level 1312 are within alower threshold value of each other may include when the vehicle is notaccelerating and when the vehicle has a level attitude. During otherconditions, a fluid transfer between degas bottle 1302 and verticalstandpipe 1304 may cause local coolant level 1314 to be greater thanbulk coolant level 1312 by at least a threshold amount. Exampleconditions which may induce such a fluid transfer may include when thevehicle is decelerating and when the vehicle has a nose-down attitude inthe embodiment where the standpipe is forward of the degas bottle in thevehicle.

During still other conditions, a fluid transfer between degas bottle1302 and vertical standpipe 1304 may cause local coolant level 1314 tobe less than bulk coolant level 1302 by at least a threshold amount.Example conditions which may induce such a fluid transfer may includewhen the vehicle is accelerating and when the vehicle has a nose-upattitude in the embodiment where the standpipe is located forward of thedegas bottle in the vehicle.

In order to adjust an estimate of the local coolant level to an estimateof the bulk coolant level, vehicle acceleration and attitude estimatesmay be used to estimate the direction and magnitude of the difference incoolant levels, for example via routine 1400 at FIG. 14. Adjusting thelocal coolant level to reflect the bulk coolant level includesdetermining a compensation term as an estimate of the divergence betweenthe local standpipe level and the bulk coolant level. This compensationterm may herein be referred to as a slosh or a slosh term. The sloshterm may have an associated sign and magnitude, and may be added to theraw standpipe level to form an adjusted standpipe level estimate. Thatis, the slosh term may subtract from or add to the raw standpipe levelto form the adjusted standpipe level estimate, which estimates what thestandpipe level would be if the vehicle were level and the standpipe andbulk levels were at equilibrium. Therefore, the adjusted standpipe levelserves as an instantaneous estimate of the coolant level in the degasbottle. The bulk coolant level estimate may then be updated based on theadjusted standpipe level estimate. Executing routine 1400 during ameasurement period may be based on whether a valid coolant level readingexists for the measurement period. For example, routine 1400 may beexecuted during measurement periods in which a raw standpipe coolantlevel has been determined, and may not be executed during measurementperiods wherein the coolant level readings have been flagged as invalid,such as at 1128 in routine 1100.

Routine 1400 begins at 1402, where the engine controller receives a rawlocal coolant level estimate for the current measurement period. The rawlocal coolant level estimate may be determined by a separate routinesuch as routine 1100 at FIG. 11. The raw level estimate is used later inroutine 1400, in combination with a slosh term, to determine a bulkcoolant level estimate. After receiving the raw coolant level estimate,routine 1400 proceeds to 1404, where estimates of longitudinalacceleration and longitudinal attitude may be determined. Longitudinalacceleration estimates may be based on data from an accelerometer, oralternatively from a time derivative of velocity sensor measurements.Longitudinal attitude estimates may be based on data from varioussensors. Similarly, at 1406, the controller may determine estimates forthe lateral acceleration and lateral attitude of the vehicle. Lateralacceleration estimates may be based on data from an accelerometer, oralternatively may be calculated from velocity and wheel speedmeasurements. Lateral attitude estimates may be based on data fromvarious sensors.

Based on the estimates of acceleration and attitude in both thelongitudinal and lateral directions made at 1404 and 1406, an expectedor predicted slosh term may be determined via a transfer function. Inone example, the transfer function may be expressed by the followingequation:Expected Slosh=(Long. Gain)*[(Long. Acc. %)*(Long. Acc.)+(1−Long. Acc.%)*(Long. Att.)]+(Lat. Gain)*[(Lat. Acc. %)*(Lat. Accel.)+(1−Lat. Acc.%)*(Lat. Att.)],where Long. Gain and Lat. Gain are weighting factors for thelongitudinal and lateral slosh estimates, Long. Acc. % and Lat. Acc. %are weighting factors which weight the relative contributions ofacceleration and attitude in the slosh estimate for each direction,Long. Acc. is an estimated longitudinal acceleration, Long. Att. is anestimated longitudinal attitude, Lat. Acc. is an estimated lateralacceleration, and Lat. Att. is an estimated lateral attitude.Acceleration estimates may be in units of distance per squared unittime, while attitude estimates may be in units of degrees inclination orstatic grade percent in that axis. The determination of longitudinal andlateral gains may be based on correlation to flat groundnon-accelerating data versus tilt table data, or based on vehicle datataken at a span of accelerations and static attitudes, and mayrespectively be in units of percent contribution of correlation. Therelative weighting of acceleration and attitude may be determined basedon the same correlation data using a method of data fitting (e.g, leastsquares estimation).

After determining a predicted slosh term, the adjusted standpipe coolantlevel estimate (that is, the raw level estimate plus the predicted sloshterm) may be above or below the physical range of the standpipe (asearlier described with reference to FIG. 11). In these examples, thepredicted slosh may be adjusted based on the physical range of thestandpipe. In one example, if the predicted slosh and the raw standpipelevel estimate add to be greater than the height of the standpipe,adjusting the predicted slosh based on the physical range of thestandpipe may include clipping the predicted slosh so that the adjustedstandpipe coolant level estimate is at upper threshold of the physicalrange. In another example, if the predicted slosh plus the raw standpipelevel estimate add to be less than the reservoir height, adjusting thepredicted slosh may include clipping the slosh estimate so that theadjusted standpipe coolant level estimate is at the lower threshold ofthe physical range.

In addition to an expected slosh term, an actual slosh term may beestimated at 1412. An estimate of actual slosh may be determined basedon a comparison of the raw standpipe coolant level estimate to a bulklevel estimate. In one example, the actual slosh may be the differencebetween the raw standpipe coolant level in the current measurementperiod and the most recent bulk level estimate.

Based on a comparison between an expected slosh and an actual slosh, apresumed slosh term may be determined at 1414. In one example,determining a presumed slosh may include, in the signed direction ofexpected slosh, choosing the lower absolute value of actual slosh andthe compensated level as the presumed slosh. This example is furtherexplained below, with reference to FIG. 16. In a further example, ifboth the unclipped expected slosh and actual slosh are within thephysical range of the standpipe and the magnitude of expected slosh isgreater than the magnitude of actual slosh, the expected slosh may beclipped based on the actual slosh, then applied as the presumed slosh.This example is further explained below, with reference to FIG. 17.

After determining a presumed slosh for the measurement period, thepresumed slosh may be applied to the raw standpipe level estimate at1416 to determine the adjusted standpipe coolant level estimate. Thebulk coolant level estimate may then be updated based on the adjustedstandpipe coolant level estimate at 1418. In one example, a filter maybe used to integrate the adjusted standpipe coolant level estimate fromthe current measurement period into the long term bulk coolant levelestimate. Filtering the adjusted standpipe level estimate may includefiltering through a low-pass filter based on a variable time constant,the time constant determined based on sign and magnitude of differencebetween the instantaneous slosh compensated reading and the long termbulk level estimate, as well as on the amount of time between last validreading and current valid and slosh compensated reading. In this way,transient changes in coolant level may be smoothed out, and a steadierestimate of the bulk coolant level may be formed.

Routine 1400 then proceeds to 1420, where sensor diagnostics may beperformed based on a comparison of the expected slosh and actual sloshterms for the measurement. In one example, an expected slosh integraland an actual slosh integral may be respectively updated based on theexpected slosh and actual slosh terms for the measurement period. Theseintegrals may be incremented whenever an expected slosh or actual sloshis detected, and may be decremented by a fixed amount each measurementperiod. Sensor degradation may be made based on the ratio of the twointegrals, and is further described with reference to FIG. 15.

FIG. 15 provides a routine 1500 for determining whether an ultrasoniclevel sensor in a vertical standpipe (such as ULS 362 of FIG. 3) isdegraded. The routine is based on a comparison of amounts of expectedslosh and actual slosh accumulated over time. The accumulation of theamounts of expected slosh and actual slosh may be characterized by anexpected slosh integral and an actual slosh integral. By comparing theseintegrals, an engine controller may determine whether more or less sloshthan expected has been detected over time, and under some conditions mayindicate degradation of the sensor based on this comparison.

Routine 1500 begins at 1502, where the value of the expected sloshintegral may be incremented if expected slosh has been detected for themeasurement period. For example, motion parameters may indicate anamount of expected slosh at 1408 in FIG. 14, and the expected sloshintegral may be incremented by an amount based on the amount of expectedslosh in the measurement period. Similarly, if actual slosh has beendetected for the measurement period, the value of the actual sloshintegral may be incremented at 1504. The amount by which the actualslosh integral is incremented may be based on the amount of actual sloshdetected. Based on a comparison of the two integrals, the ultrasoniclevel sensor may be determined to be degraded due to excessive noise ifa first set of conditions is met, and may be determined to be degradeddue to a stuck reading if a second set of conditions is met.

At 1506, each of the expected slosh integral and the actual sloshintegral may be decremented by a predetermined amount. In one example,each integral may be decremented by the same fixed amount eachmeasurement period, the fixed amount determined based on a baselineamount of integration per loop measured under verified levelnon-accelerating conditions where there is less than a lower thresholdamount of slosh, thereby establishing a base noise level of thecalculation. In another example, the actual slosh integral may bedecremented by a first fixed amount each measurement period, and theexpected slosh integral may be decremented by a second fixed amount eachmeasurement period, the first amount determined based on a baselineamount of integration per loop measured under verified levelnon-accelerating conditions where there is no or limited slosh, therebyestablishing a base noise level of the calculation, and the secondamount a smaller fraction (e.g., 80%) of the first amount. In this way,the expectation integral decrement rate is biased toward expecting someamount of slosh during each measurement period. In a further example,each integral may be decremented by the same variable amount eachmeasurement period, the variable amount for each measurement perioddetermined based on the same conditions as above to determine abaseline, and further including varying the decrement rate based on amagnitude of expected slosh, calculated instantaneously based on theweighted combination of longitudinal and lateral acceleration andattitude changes. In a still further example, the expected sloshintegral may be decremented by a first variable amount each measurementperiod, and the actual slosh integral may be decremented by a secondvariable amount each measurement period, the first and second amountsdetermined based on the same principles as the other combinationexamples above. Other possibilities for decrementation may include oneintegral being decremented by a fixed amount, and the second integralbeing decremented by a variable amount.

After each integral has been incremented based on the amounts of sloshdetected during the measurement period, and decremented based on one ofthe above example baseline noise compensations above or a similarcompensation, a ratio of the actual slosh integral and the expectedslosh integral may be determined at 1508. In one example, the actualslosh integral amount may be divided by the expected slosh integralamount, and this number may be applied as the ratio of the two.

At 1510, this ratio is compared to an upper threshold. The upperthreshold ratio may be determined based on measuring the largest ratiosseen on a test that physically stresses the amount of slosh within thestandpipe (e.g., placing a vehicle on a shaker table and operating thetable at a variety of amplitudes/frequencies to find worst case inresonance with slosh reading). Alternatively, the upper threshold ratiomay be determined based by directly instituting an electrical noisesignal on the level sensor input into the electronic control module. Theratio being greater than the upper threshold may indicate that moreslosh was detected than was expected by more than a threshold amount. Ifthe ratio is greater than the upper threshold, routine 1500 may proceedto 1512, where the controller may indicate that the ultrasonic levelsensor is degraded due to noisiness. After indicating degradation of thesensor due to noisiness, routine 1500 terminates.

If the ratio is not greater than the upper threshold, routine 1500proceeds to 1514, where the ratio from 1508 may be compared to a lowerthreshold. The lower threshold may be determined based on performing oneor more drive cycles (e.g., one of FTP or US06) take place at a nearempty, near full and half full standpipe/degas bottle level on flatground before each test respectively. These tests include clampingeither the upper or lower standpipe hose completely shut as to preventgas or fluid exchange during the drive cycle. Thus, the lower thresholdmay represent a baseline level of noise. The lowest ratios seen fromthese tests are used to set the lower threshold level. The ratio beingless than a lower threshold may indicate that less slosh was detectedthan was expected by more than a threshold amount.

If the ratio is less than the lower threshold, routine 1500 may proceedto 1516, where the controller may indicate that the ultrasonic levelsensor may be stuck or that fluid transfer between the degas bottle andthe vertical standpipe may be physically impeded. The controller maydistinguish between these two degradations based on waiting for both apredetermined period of time or distance travelled before determining ifthe fault disappeared, thus suggesting the ratio is low due toobstruction. If the ratio is not less than the lower threshold, routine1500 proceeds to 1518, where sensor degradation is not indicated, androutine 1500 then terminates.

FIG. 16 provides a control scheme 1600 for determining an assumed slosh,applying the assumed slosh to the raw standpipe coolant level todetermine an adjusted standpipe coolant level, and updating a bulkcoolant level based on the adjusted standpipe coolant level. Data frommotion sensors such as acceleration sensor 1602, attitude sensor 1604,vehicle speed sensor 1606, and wheel speed sensor 1608 may be used todetermine longitudinal acceleration, lateral acceleration, longitudinalattitude, and lateral attitude at 1610. In some examples, bothlongitudinal and lateral accelerations may be determined based on datafrom a single acceleration. In other examples, longitudinal and lateralaccelerations may be determined from separate acceleration sensors.Similarly, longitudinal and lateral attitudes may be determined by oneor more attitude sensors. At 1612, variables 1610 are used as input to afunction determining an expected slosh 1614. In one example, function1612 may be expressed by the equation described above with reference toFIG. 14. Expected slosh 1614 may then be clipped at 1620, andadditionally an expected slosh integral 1644 may be incremented based onexpected slosh 1614. Expected slosh integral 1644 is described below infurther detail. Clip 1620 may be based on the physical range of thestandpipe 1618, as described above with reference to FIG. 14, which maybe stored in and accessed from the memory of controller 1616. Clippingexpected slosh 1614 at 1620 results in a rationalized expected slosh1622.

In addition to rationalized expected slosh 1622, an actual slosh 1628may be determined based on the difference 1626 of the raw standpipecoolant level 1624 and the bulk coolant level 1625. Coolant levels 1624and 1625 may be accessed via controller 1616. Actual slosh integral 1646may be incremented based on actual slosh 1628. Actual slosh integral isdescribed below in further detail. The rationalized expected slosh 1622and the actual slosh 1628 may serve as inputs to compensator 1630.Compensator 1630 may determine a presumed slosh 1632 based on inputs1622 and 1628.

In one example, compensator 1630 may compare sloshes 1622 and 1628,applying rationalized expected slosh 1622 as presumed slosh 1632 under afirst set of conditions, and applying actual slosh 1628 as presumedslosh 1632 under a second set of conditions. For instance, the first setof conditions may include sloshes 1622 and 1628 being of the same sign(that is, both estimate a positive amount of slosh or both estimate anegative amount of slosh), and both sloshes being within the physicalrange of the standpipe 1618, but rationalized expected slosh 1622 beingof a lesser magnitude than actual slosh 1628. The second set ofconditions may include sloshes 1622 and 1628 being of the same sign, andboth sloshes being within the physical range of the standpipe 1618, butactual slosh 1628 being of a lesser magnitude than rationalized expectedslosh 1622.

In another example, compensator 1630 may adjust rationalized expectedslosh 1622 based on actual slosh 1628, and apply the adjusted amount ofslosh as presumed slosh 1632. Adjusting rationalized expected slosh 1622based on actual slosh 1628 may include, if expected slosh 1622 isgreater than actual slosh 1628, applying only a portion of rationalizedexpected slosh 1622 as presumed slosh 1632. The actual slosh 1628 may beless than the rationalized expected slosh 1622 if fluid exchange betweenthe degas bottle and the standpipe is physically impeded. By applyingonly a portion of the rationalized expected slosh as the presumed sloshwhen the rationalized expected slosh is greater than the actual slosh,the accuracy of a bulk coolant level estimate may be improved. Ifexpected slosh 1622 is less than actual slosh 1628, adjustingrationalized expected slosh 1622 based on actual slosh 1628 may includecompensating only by the amount expected, the expected amount aconservative amount based on a predetermined mapping of the vehiclespropensity to slosh.

Presumed slosh 1632 may be applied to raw standpipe coolant level 1634to determine adjusted standpipe coolant level 1638. In one example,applying presumed slosh 1632 to raw standpipe coolant level 1634 mayinvolve the addition of presumed slosh 1632 to raw standpipe coolantlevel 1638. Filter 1640 may update bulk coolant level 1639 (accessiblevia controller 1616) based on adjusted standpipe coolant level 1638,thereby determining the updated bulk coolant level estimate 1642.Filtering bulk coolant level 1639 based on adjusted standpipe coolantlevel 1638 may include determining a time constant based on the overallmagnitude of slosh compensation being applied to the instantaneous levelreading (e.g., more filtering if more compensation applied), and furtherbased on the signed magnitudes of adjusted standpipe coolant level 1638level reading and bulk coolant level 1639. Coolant state 1660 may thenbe updated based on updated bulk coolant level estimate 1642, asdescribed in further detail with reference to FIG. 18.

Returning to expected slosh integral 1644, the integral may beincremented based on the magnitude of expected slosh 1614. For example,expected slosh integral 1644 may be incremented by an amount directlyproportional to expected slosh 1614. Similarly, actual slosh integral1646 may be incremented based on the magnitude of actual slosh 1628.Expected slosh integral 1644 and actual slosh integral 1646 may bedecremented at 1645 and 1647, respectively. In one example, eachintegral may be decremented by the same fixed amount each measurementperiod, the fixed amount determined based on the compensation methodsdescribed at 1506 of FIG. 15. After integrals 1644 and 1646 have beendecremented at 1645 and 1647, sensor state 1650 may be determined atleast in part based on the integrals. In one example, a ratio of actualslosh integral 1646 the actual slosh integral amount may be divided bythe expected slosh integral amount, and determining the state of thesensor may be based on a comparison of this ratio to both an upperthreshold and a lower threshold.

FIG. 17 provides illustrations of various slosh conditions thatcompensator 1630 of FIG. 16 may encounter. Plots 1710, 1720, 1730, 1740show fluid levels based on estimated sloshes (dashed lines) and actualsloshes (solid lines). At 1710, expected slosh 1712 is positive andgreater than the maximum physical level of the standpipe, while theactual slosh 1714 is positive and at the maximum physical level of thestandpipe. During such a condition, actual slosh 1714 may be applied asthe presumed slosh for the measurement period as it may be the case thata temporary obstruction in a hose (e.g., a fluid trap) or the actual endof the vertical standpipe (e.g., due to stackup) has physically limitedthe slosh amount.

At 1720, both expected slosh 1722 and actual slosh 1724 are positive andwithin the physical range of the standpipe, and the magnitude ofexpected slosh 1722 is greater than the magnitude of actual slosh 1724.In such a condition, only a portion of expected slosh may be applied asthe presumed slosh for the measurement period.

At 1730, both expected slosh 1732 and actual slosh 1734 are positive,and the magnitude of expected slosh 1732 is less than that of actualslosh 1734. In such a condition, expected slosh 1732 may be applied asthe presumed slosh for the measurement period.

At 1740, both expected slosh 1742 and actual slosh 1744 are negative andwithin the physical range of the standpipe. During such a condition,actual slosh 1744 may be applied as the presumed slosh for themeasurement period, as a temporary hose obstruction (e.g., a fluid trap)may be present. By choosing the slosh with the lower magnitude,preventing overcompensation for a model of expected slosh withinaccurate estimates of the gain of acceleration or attitude to slosh,or for a temporarily obstructed hose, may be achieved.

FIG. 18 depicts a routine 1800 for updating a coolant state based on thebulk coolant level estimate and the current coolant state. The updatedbulk coolant level estimate may correspond to one or more coolantstates. For example, the bulk coolant level estimate may be one of OK,LOW, EMPTY, UNKNOWN/DEGRADED, and FAULTED. In this example, the bulkcoolant level estimate may be OK if it is above a higher thresholdlevel, and may be LOW if it is below the higher threshold but above alower threshold. Additionally, the bulk coolant level estimate may beEMPTY if it is below a lower threshold. Furthermore, a middle thresholdmay be included, as described below with reference to 1822 and 1826. Insome examples, routine 1800 may only update the coolant state if a bulkcoolant level estimate corresponding to a different coolant state haspersisted for longer than a threshold duration. Routine 1800 may beexecuted with a coolant system such as that described in FIGS. 2-9, andmay be executed during each measurement period in which a valid bulkcoolant level estimate is determined, after the bulk coolant levelestimate has been updated (such as via routine 1400 or control scheme1600).

Routine 1800 begins at 1802, where bulk coolant level estimate 1804,current coolant state 1806, and temperature data 1808 are received froman engine controller. At 1810, the controller may determine whether thecoolant system is faulted. Conditions that indicate the coolant systembeing faulted may include a lost connection to the controller areanetwork, zero echoes being received for the measurement period, or anengine temperature being above an upper threshold. If the coolant systemis determined to be faulted at 1810, routine 1800 proceeds to 1812,where the controller may indicate that the coolant level is FAULTED.Routine 1800 may then update the coolant state based on the currentcoolant level and the current coolant state at 1832. If the coolantsystem is determined to not be faulted 1810, routine 1800 proceeds to1814.

Continuing at 1814, the controller may determine if the ultrasonic levelsensor is degraded or if the coolant level is unknown for the currentmeasurement period. Either condition may correspond to a coolant levelof UNKNOWN/DEGRADED. An ultrasonic level sensor may be determined to bedegraded if, for example, the engine controller had previously indicateda noisy sensor or a stuck sensor at 1512 or 1516 in routine 1500.Alternatively, sensor degradation may be determined if the expectedamount of slosh suggests that the level of vehicle acceleration/attitudeoccurring instantaneously is too high to compensate for (i.e., if theexpected slosh indicates an out of range transient reading). The coolantlevel may be determined to be UNKNOWN/DEGRADED if, for example, the rawstandpipe coolant level estimate had been outside of the physical rangeof the standpipe by more than a threshold amount, as described withreference to 1126 at FIG. 11, or alternatively if the expected slosh forthe measurement period is greater than a threshold magnitude, thethreshold magnitude determined based on the expected slosh being morethan a percentage of total standpipe height (e.g., plus or minus 25 mmon a 100 mm standpipe). Additionally, the coolant level may bedetermined to be UNKNOWN if an insufficient number of valid pulse echoesare returned but not for a enough measurement periods to set the coolantlevel to a detected FAULTED state for the sensor. If the ultrasoniclevel sensor is determined to be degraded or if the bulk coolant levelestimate is determined to be unknown for the measurement period, thecontroller may indicate that the coolant level is UNKNOWN/DEGRADED at1816. Routine 1800 may then update the coolant state based on thecurrent coolant level and the current coolant state at 1832, asdescribed below in further detail. Returning to 1814, if conditions donot indicate that the ultrasonic sensor is degraded and bulk coolantlevel estimate is known, routine 1800 proceeds to 1818.

At 1818, the bulk coolant level estimate is compared to an upperthreshold level to determine whether the coolant level is OK. The upperthreshold level may be determined based on the pre-determinedcorrelation of the sensor measurement when a vehicle that is stationaryon level ground is filled to the lowest acceptable factory-recommendedfill level. If the bulk coolant level estimate is above the upperthreshold level, the current coolant level may be indicated as OK at1820. In some examples, the current coolant level may only be indicatedas OK if the bulk coolant level estimate is above the upper thresholdlevel by more than a predetermined amount. Routine 1800 may then updatethe coolant state based on the current coolant level and the currentcoolant state at 1832, as described below in further detail. Returningto 1818, if the bulk coolant level estimate is not determined to beabove the upper threshold level, routine 1800 proceeds to 1822.

At 1822, the bulk coolant level estimate is compared to a middlethreshold level to determine whether the coolant level is LOW. Note thatat 1822, the bulk coolant level estimate has already been determined tobe below the upper threshold level. The middle threshold level mayherein also be referred to as the LOW threshold level. If the bulkcoolant level estimate is determined to be above the LOW threshold, thecoolant level may be indicated to be LOW at 1824. Routine 1800 may thenupdate the coolant state based on the current coolant level and thecurrent coolant state at 1832, as described below in further detail.Returning to 1822, if the bulk coolant level estimate is not determinedto be above the middle threshold level, routine 1800 proceeds to 1826.

At 1826, the bulk coolant level estimate is compared to a lowerthreshold level to determine whether the coolant level is LOW or EMPTY.The lower threshold level may herein also be referred to as the EMPTYthreshold level. Note that at 1826, the bulk coolant level estimate hasbeen determined to be below the LOW threshold level. Thus, at 1826 it isdetermined if the bulk coolant level estimate is between the LOW andEMPTY threshold levels, or if it is below the EMPTY threshold level. Ifthe bulk coolant level estimate is below the EMPTY threshold level, thecoolant level is indicated to be EMPTY at 1830. Routine 1800 may thenupdate the coolant state based on the current coolant level and thecurrent coolant state at 1832, as described below in further detail.Returning to 1826, if the bulk coolant level estimate is determined tobe above the lower threshold level, routine 1800 proceeds to 1828, wherethe coolant level is determined based on the coolant state.

Specifically, at 1828 if the bulk coolant level estimate is above theEMPTY threshold level but less than the OK threshold and the coolantstate is EMPTY, the controller may indicate that the coolant level isEMPTY. If the bulk coolant level estimate is above the EMPTY thresholdand the coolant state is OK, the controller may indicate that thecoolant level is OK. In this way, the coolant state may not be changedfrom EMPTY to LOW until the bulk coolant level estimate is above the OKthreshold.

At 1832, the coolant state may be updated based on coolant level. Insome examples, the coolant state may only change after a coolant levelindicating a new coolant state has persisted for a threshold duration.In this way, by not changing the coolant state based on short-termfluctuations in coolant level about a threshold, the consistency ofcoolant state may be improved. Because changing a coolant state mayinclude adjusting engine parameters, a consistent coolant state mayimprove engine operating conditions. In one example, the thresholdduration may be based on one or more of a threshold number ofmeasurement periods, engine coolant temperature, engine speed, vehiclespeed, estimated coolant level, and current coolant state. Thisthreshold duration may differ for each coolant state, or alternativelyfor each set of coolant states. As a non-limiting example, adjusting thecoolant state from OK to LOW may require indicating a LOW bulk coolantlevel for a different threshold number of measurement periods thanadjusting the coolant state from LOW to EMPTY requires indicating anEMPTY bulk coolant level.

In some examples, restrictions may be placed on changing coolant states.For example, the coolant state may only change to EMPTY if the coolantlevel has been indicated as EMPTY for a first threshold number ofmeasurement periods, not been indicated as being one of LOW or OK for asecond threshold number of measurement periods, the second thresholdnumber greater than the first. In this way, transient dips into an EMPTYrange may be rejected from falsely detecting EMPTY state. Additionally,the coolant state may only change to EMPTY after the vehicle movementhas been detected and the vehicle is determined to be in gear during thecurrent key cycle. In this way, an operator of the vehicle may fill thesystem with coolant and allow it to move to a detected full OK statewithout having to continuously reset the control module in order to exitthe EMPTY state if that is a requirement.

At 1834, engine operating parameters are adjusted based on the updatedcoolant state. In some examples, the coolant state may not have beenupdated for the measurement period, and engine parameters may bemaintained from the previous measurement period. However, if the coolantstate has been updated, restrictions may be placed on or lifted fromengine operating parameters. For example, if the coolant state wasupdated from OK to EMPTY, commands for engine loads above a thresholdload may be disallowed while the coolant state remains EMPTY to preventoverheating of engine components. Adjusting engine operating parametersbased on coolant state is described in further detail below, withreference to FIG. 19. Routine 1800 then terminates.

FIG. 19 provides a routine 1900 for restricting engine operatingparameters based on the coolant state determined by routine 1800.Routine 1900 may be executed for each measurement period, for example at1834 of routine 1800. An engine controller may include a set ofrestriction modes, and may select a mode from the set of modes based onthe coolant state and the duration for which the coolant system has beenin that coolant state. Selecting a restriction mode may include one ormore of restricting an engine load to be below an upper threshold,reducing an injection pulse-width for one or more fuel injectors by athreshold amount, entirely eliminating fuel injection for one or morefuel injectors, forcing the engine to operate in an idle mode, anddisplaying messages to the vehicle operator indicating information aboutthe bulk coolant level and about the selected restriction mode.Displaying messages to the vehicle operator may include indicating anylimits placed on engine/transmission operation (e.g., limits on power,torque, engine speed, available gears, etc.), as well as indicating thataddition of coolant is needed if in a LOW level state, or indicating animmediate need to stop and add coolant if in an EMPTY level state.Selecting a restriction mode may also include tracking the duration forwhich the engine has operated under the current restriction mode.

Routine 1900 begins at 1902, where the coolant state is retrieved fromthe engine controller. Retrieving a coolant state may include retrievinga duration for which the current coolant state has been active. At 1904,it is determined whether the coolant state was changed during thecurrent measurement period. If the coolant state was changed, routine1900 proceeds to 1908, where a restriction mode may be selected based onthe coolant state and the duration in the coolant state. Selecting arestriction mode is described below in further detail. If the coolantstate was not changed during the current measurement period, routine1900 proceeds to 1906.

At 1906, the duration for which the current coolant state has beenactive is compared to one or more threshold durations. Additionally, theduration for which the current restriction mode has been active may becompared to one or more threshold durations. If a threshold duration hasnot been reached, routine 1900 proceeds to 1910, where operation in thecurrent restriction mode may be maintained. Routine 1900 may thenterminate.

Returning to 1906, if a threshold duration has been reached, routine1900 proceeds to 1908, where a restriction mode may be selected based onthe coolant state and the duration in the coolant state. Note that 1908may also be reached if the coolant state was changed during the currentmeasurement period. In one example, the set of restriction modes theengine controller may select from may include at least a first, second,and third mode. In the first restriction mode, the engine controller mayonly indicate to the vehicle operator that the bulk coolant level is lowand that the vehicle should be taken to a dealership, without placingrestrictions on engine operating parameters such as engine load and fuelinjection. Selecting the second restriction mode may include placing anupper threshold on engine loads and cutting fuel injection from one ormore cylinders by eliminating a fuel injection pulse-width for thosecylinders. The third restriction mode may include the restrictions ofthe second mode, and may further restrict the engine to only operatingin an idle mode.

In some examples, operation with a particular restriction mode may notbe exited until certain conditions are met. In one example, the secondrestriction mode may only be exited upon the restarting the engine. Suchan example may also include only exiting operation with the thirdrestriction mode upon visiting a dealership. In such examples, selectinga restriction mode at 1908 may also be based on the current restrictionmode. For example, the engine may be operating in the second restrictionmode and current coolant state may indicate operating in the firstrestriction mode. However, the engine controller may not select tooperate in the first mode based on currently operating in the secondrestriction mode.

Selecting a restriction mode at 1908 may include, if the coolant stateis LOW or EMPTY, selecting the first restriction mode mentioned above.Selecting the first restriction mode may include operating in the firstrestriction mode for a threshold duration, and selecting one of thesecond and third restriction modes based on engine conditions after thethreshold duration.

Selecting a restriction mode at 1908 may alternately include, if thecoolant state has been EMPTY for more than a threshold duration,operating in the second restriction mode. Selecting the secondrestriction mode may include operating in the second restriction modefor a threshold duration, and selecting the third restriction mode afterthe threshold duration. The engine controller may also select to operatein the second restriction mode if the last known state of the system wasEMPTY and the current state has been UNKNOWN/DEGRADED for a thresholdduration, as this condition may be considered functionally equivalent toEMPTY.

Selecting a restriction mode at 1908 may further include, if the coolantstate has been EMPTY for more than a threshold duration, operating inthe third restriction mode. Selecting the third restriction mode mayinclude operating in the third restriction mode until the vehicle hasbeen taken to a dealership. The engine controller may only select tooperate in the third restriction mode when the coolant state isconfirmed EMPTY. In this way, engine operating parameters may berestricted to avoid overheating in the engine.

The technical effect of using a system configured with a coolantoverflow container having an internal recess to hold fluid and avertical, hollow tube positioned external to the container and includingan internal recess to hold fluid, wherein a bottom-most level of therecess is positioned vertically below a bottom-most level of theinternal recess of the container and having a sensor coupled to thebottom-most level of the internal recess of the tube, is that thecoolant level in the container can be inferred more accurately. Byfluidically coupling the standpipe to the overflow container, fluidlevels are allowed to equilibrate in the two containers enabling thefluid height in the container to be reflected in the fluid height of thevertical tube. By estimating the fluid height in the vertical tube usingthe transmission of ultrasonic signals and detection of their echoes,the sensor output is not grossly affected by distortions that may affectbulk fluid reservoirs, such as temperature and motion variations. Inaddition, the technical effect of adjusting an estimate of fluid levelin the vertical, hollow standpipe based on vehicle motion parameters isthat the fluid level can be better compensated for variations due toslosh, and a vehicle actuator can be adjusted in response to the moreaccurate fluid level estimate. This also reduces erratic fluid levelestimates generated due to fluid slosh. By limiting engine power basedon the estimated fluid level over a duration, engine overheating due tolow coolant levels in the reservoir can be reduced. In addition,unwanted triggering of failure modes due to false low readings can alsobe averted. By enabling a processor to estimate the fluid level in thestandpipe based on raw data and/or processed data generated by theultrasonic sensor, estimation accuracy and reliability is improved. Morespecifically, the technical effect of receiving each of unprocessed, rawecho times and processed fluid level data from the sensor coupled in thevertical tube, and generating a fluid level estimate based on the rawecho times and vehicle sensor data during some conditions whilegenerating the fluid level estimate based on the processed data duringother conditions raw data that is unreliable can be discarded and notused to estimate the fluid level. This increases the weightage ofreliable data in the final estimation. In addition, sensor power outputcan be optimized based on the nature of raw data collected at thesensor. Specifically, the technical effect of periodically transmittinga sensor signal from a bottom to a top of the vertical tube, receivingan echo of the transmitted signal at the sensor and adjusting a power ofthe periodically transmitted signals based on an average durationelapsed between the transmitting and the receiving, is that sensor powercan be adjusted to improve the number and quality of first order echoesgenerated while decreasing the number of second order echoes generated.This improves the accuracy and reliability of the fluid level estimatewhile also providing power reduction benefits. Overall, coolant levelsin an engine cooling system can be better monitored, improve engineperformance.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method, comprising: estimating fluidlevel in a coolant reservoir based on a sensor coupled in a verticalstandpipe aligned parallel to the reservoir, the standpipe fluidicallycoupled to the reservoir at each of a top and bottom location; andlimiting engine power based on the estimated fluid level.
 2. The methodof claim 1, wherein limiting based on the estimated fluid level includeslimiting based on the estimated level relative to each of a first, upperthreshold and a second, lower threshold.
 3. The method of claim 2,wherein the limiting includes limiting by a first amount when theestimated fluid level is below the first threshold and above the secondthreshold, and limiting by a second, different amount when the estimatedfluid level is below each of the first and second threshold.
 4. Themethod of claim 3, when the second amount is larger than the firstamount, and wherein the second amount is adjusted based on a durationfor which the estimated fluid level remains below the second threshold.5. The method of claim 4, further comprising indicating degradationbased on the estimated fluid level.
 6. The method of claim 5, whereinthe indicating includes setting a first diagnostic code when theestimated fluid level is above the first threshold, setting a seconddiagnostic code when the estimated fluid level is below the firstthreshold and above the second threshold, and setting a third diagnosticcode when the estimated fluid level is below each of the first andsecond threshold.
 7. The method of claim 1, wherein the estimating fluidlevel in a coolant reservoir based on a sensor includes transmitting anultrasonic signal from the sensor towards a top of the standpipe,receiving an echo of the ultrasonic signal at the sensor upon reflectionoff a cap coupled to the top of the standpipe, estimating a durationelapsed since the transmission of the ultrasonic signal and receipt ofthe echo at the sensor, and estimating the fluid level in the coolantreservoir based on the estimated duration.
 8. The method of claim 7,further comprising predicting fluid slosh based on vehicle motion, andadjusting the estimated fluid level with a compensation term based onthe predicted fluid slosh.
 9. The method of claim 8, further comprisingestimating actual fluid slosh based on a transient change in sensoroutput, and wherein the compensation term is based on the predictedfluid slosh relative to the estimated actual fluid slosh.
 10. A methodfor an engine, comprising: differentiating between states of a fluidlevel in a coolant reservoir based on output from a sensor coupled at abottom-level of an internal recess of a vertical standpipe, thestandpipe positioned adjacent to the reservoir and further fluidicallycoupled to the reservoir at each of a top and bottom location, theoutput estimated over a duration.
 11. The method of claim 10, whereinthe duration is adjusted based on engine coolant temperature, theduration decreased as engine coolant temperature increases.
 12. Themethod of claim 10, wherein the differentiating is further based on achange in the sensor output responsive to vehicle motion-induced slosh.13. The method of claim 12, wherein differentiating further based onslosh includes differentiating further based on expected slosh relativeto estimated slosh, the expected slosh based on vehicle lateral andlongitudinal acceleration, the estimated slosh based on the change inthe sensor output.
 14. The method of claim 10, further comprisinglimiting engine power differently based on each state of fluid level inthe coolant reservoir.
 15. The method of claim 14, wherein the states offluid level include: a first degraded state where the reservoir isempty; a second degraded state where the reservoir fluid level is low; athird degraded state where the reservoir fluid level is unknown; and afourth degraded state where the sensor is faulty.
 16. The method ofclaim 15, wherein the limiting differently includes: in response to thefirst degraded state, limiting engine power by a first amount; inresponse to the second degraded state, limiting engine power by a secondamount; in response to the third degraded state, limiting engine powerby a third amount; and in response to the fourth degraded state,limiting engine power by a fourth amount.
 17. The method of claim 10,wherein the differentiating is further based on one or more of coolanttemperature and exhaust temperature.